Neurologic injury under general anesthesia in the beach chair position is believed to result from cerebral hypoperfusion.1 We hypothesize that brain hypoperfusion in this circumstance is caused by blood pressure monitoring that does not reflect of cerebral perfusion pressure. Maintenance of arterial blood pressure above an individual's lower limit of cerebral blood flow autoregulation would prevent this devastating complication. Near infrared spectroscopy can be used to continuously monitor autoregulation with the cerebral oximetry index (COx), a moving linear correlation coefficient between cortical tissue oxygen saturation and arterial pressure. We hypothesize that subjects in the beach chair position have impaired cerebral blood flow autoregulation compared with subjects undergoing surgery in the lateral decubitus supine position. We will test this hypothesis by comparing CBF autoregulation data, including the percentage of time patients undergoing elective surgery have abnormal autoregulation, in the beach chair position versus supine position. We will establish the range of arterial pressure required to maintain autoregulation in the two groups. Cerebral autoregulation results will be assessed for a relationship with postoperative neurocognitive dysfunction and with serum glial fibrillary acid protein levels, a biomarker of brain injury.